Abstract

HERMAN, H.  and  MEYER, J.P.. Heat transfer augmentation of a spiralled tube inside the annulus of a tube-in-tube heat exchanger. R&D j. (Matieland, Online) [online]. 1998, vol.14, pp.43-48. ISSN 2309-8988.

The potential of a simple and inexpensive method of heat augmentation that could be manufactured relatively easily by small manufacturing companies is investigated. It consists of a tube that is turned spirally and tightly around the outer surface of the inside tube of a tube-in-tube heat exchanger. The aim is to increase the heat transfer between the flow in the inner tube and the flow in the annulus by increasing the heat transfer coefficient in the annulus. This investigation was conducted with measurements taken at five different twist angles: the first without a spiralled tube and the rest twisted at angles corresponding to a pitch 1D, 2D, 3D, and 4D. The Nusselt number and friction factor in the annulus of each case study were measured as functions of the Reynolds number, while the Prandtl number was kept constant, and for each heat exchanger configuration an equation was deduced that describes this functional relationship. It was found in general that the geometry considered is appropriate for heat transfer enhancement and that the highest heat transfer per unit pumping power occurs at a pitch of 4D. It is recommended that more work should be conducted on this geometry, specifically at pitches of 4D and higher.

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